<html lang="zh">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>
<body>
    <script>
      var str ="hello world";
       //非空字符进行布尔判断时会被理解为布尔值true
       if(str){
           alert("值为真")
       }
    </script>
</body>
</html>